The invention relates to hydraulic lift mechanism wherein lift is accomplished through a continuous cyclic succession of vertical reciprocation. And the invention will be particularly described in application to the kind of vertical reciprocation involved in the pumped recovery of oil from a well casing.
My U.S. Pat. No. 4,631,918 describes oil-well pumping apparatus (a) in which a traction cylinder is mounted at the well-head for direct reciprocating operation of the polish rod from which a pumping piston is suspended in a well casing, and (b) in which hydraulic-counterweight principles of my U.S. Pat. No. 4,715,180 are employed to reduce lift-capacity requirements which would otherwise be imposed on the prime mover. In one embodiment, in which a single well is to be pumped, a pressurized hydraulic accumulator is connected to the traction cylinder via a power integrator which is so driven by the prime mover as to shuttle hydraulic fluid under pressure between the accumulator and the traction cylinder, to accomplish the traction-cylinder action necessary to drive the polish rod and its load; in another embodiment, wherein two nearby wells are to be pumped, the hydraulic accumulator is replaced by the traction cylinder for the polish rod assembly of the second well, and the pumping cycle of one well is in phase opposition to that of the other well, such that the minimum loads of the respective traction cylinders offset each other.
The disclosures of said patents are incorporated herein by reference.
The pumping systems of said U.S. Pat. No. 4,631,918 achieve substantial improvement in efficiency and economy of operation, but in the light of the present invention, such efficiency and economy are not as great as I now believe to be possible.